[Objective]To estimate the clinical value of serum high mobility group box 1(HMGB1) as a biomarker of idiopathic pulmonary arterial hypertension (IPAH).[Methods]This study included 33 patients with IPAH that were confirmed by right heart catheter in the Second Xiangya Hospital, Central South University from May 2011 to April 2015. 8 patients with IPAH were followed up for 6 months during treating with PAH-specific pharmacotherapies. All the subjects ' clinical data were collected,HMGB1 levels were determined by enzyme linked immunosorbent assay(ELISA).[Results]Serum HMGB1 levels (ng/mL) were significantly increased in patients with IPAH compared with the control group(14.8 ± 2.4 vs. 3.8 ± 1.2, P<0.001);The serum HMGB1 levels were significant?ly positive correlation with mean pulmonary arterial pressure(MPAP) and pulmonary vascular resistauce (PVR) ( r=0.864, P<0.001; r=0.460,P=0.002) in the patients with IPAH. After treating with PAH-specific pharmacotherapies for 6 month, HMGB1 levels(ng/mL) were significantly decreased(15.9±5.3 vs 11.1±2.5,P=0.021)along with the patients'MPAP(62.3±9.7 vs 54.0±8.7,mmHg)and 6-min walk distances(m)improved(368±69 vs 401±55,P<0.001).[Conclusions]Our study suggested that serum HMGB1 may be used as a biomarker of treatment response to targeted therapy, and it will be used as a biomarker in the follow-up evaluation of patients with IPAH.